This invention relates to a multi-layer parison and a multi-layer bottle each having a good heat resistance, which are made of polyester and an apparatus for and a method of manufacturing the multi-layer parison and the multi-layer bottle.
Recently, there have appeared bottles made of polyester into which liquid is poured at a temperature of 80.degree. to 90.degree. C. (hot filling) and which are pasteurized with hot water. Therefore, it is required to provide good heat resistance to the mouth portions of the bottles. Because, in general, the mouth portion of the bottle is the first portion to be contacted hot liquid at the time of hot filling, and hot water (with the shower) is poured onto the bottles from a position above the bottles.
In view of these circumstances, various attempts have been made in order to give a heat resistance to a bottle made of polyester.
Japanese Laid-Open Publication 19208/1988 discloses a typical method of providing a heat resistance to a bottle made of polyester, in which a multi-layer parison is firstly made by injecting polyester together with heat resistant resin and is expanded through a stretching blow molding.
However, in this method, only one layer of heat resistant resin is formed between two layers of polyester, and three layers of heat resistant resin are slightly formed at the end of the opening of the mouth portion of the parison. Therefore, the entire mouth portion does not have a good heat resistance.
When the above hot filling, hot shower and pasteurizing operations are performed it is required to give a much better heat resistance to a mouth portion. For this purpose, it is desired to develop a bottle including much heat resistant resin near the mouth portion of a parison.
In general, since heat resistant resin is expensive, it is desired to develop a low-cost bottle in which heat resistant resin is concentrated on the mouth portion thereof which is not stretched, on an intermediate portion between the mouth portion and the shoulder portion thereof, which is not stretched and on the shoulder portion which is directly exposed to hot shower from above, and in which heat resistant resin is not used in the body portion thereof to which a heat resistance can be provided by stretching and heat setting and not used in the bottom portion which can be formed thicker than other portions and is not exposed directly to the hot shower.
In the case of a stretching blow molding of a parison in which heat resistant resin is disposed near the mouth portion and is also disposed at the shoulder portion, and each portion of which has different rates of heat resistant resin, a part of a bottle having been formed is often whitened or clouded and is often deformed by a change with the passage of time or heat shrinkage. It is believed that this phenomenon is caused by different rates of heat resistant resin at each part of the bottle and by different rates of stretching at each part thereof.